[Patent document 1] JP-2007-6420 A
[Non-patent document 1] K. Ito and M. Takahashi, and K. Fujii: Transmission Mechanism of Wearable Devices Using the Human Body as a Transmission Channel, in “Antennas and Propagation for Body-Centric Wireless Communications (Peter S. Hall and YangHao (Eds.)),” Artech House, pp. 65-92, 2006
There is conventionally known a communications apparatus, which is attached to a user and carries out data communications (i.e., intrabody communication) with an external device contacted by the user via a communications channel partially constituted by the user's body.
For instance, Patent document 1 describes such a type of a communications apparatus equipped with two electrodes which contact a body of a user wearing the apparatus while one of the two electrodes is used as a reference electrode and the other is used as a transmission electrode.
Patent document 1 also discloses a technology that a directionality at the time of the transmission is affected by the arrangement of the electrodes. That is, when the apparatus is worn by a user in an arm such that two electrodes are aligned in an axis or direction of the arm, the efficiency is improved by about 20 dB in comparison with the case that the two electrodes are aligned in a direction orthogonal to the arm axis.
The vector indicating a direction allowing the maximum transmission efficiency is referred to as a directional vector.
The communications apparatus in Patent document 1 is a type of a wrist watch fixedly attached to an arm or the like so that the positional relation between the electrodes and the human body is constant. Alternatively, another type such as a card type is studied. In such a type, the positional relationship between the electrodes and the human body is differentiated on each occasion or each time.
It is noted that the communications apparatus can be desirably attached to a human body such that the directional vector (i.e., electrodes arrangement direction) is along the channel from the communications apparatus to an external device. However, in any type of communications apparatuses, the positional relation between the communications apparatus and the external device may change depending on attachment positions of the apparatus (right hand/left hand/chest pocket/hip pocket, etc.), users' postures (standing position/seating position), users' portions contacting external devices of communications partners (right hand/left hand, etc.) In addition, the wrist watch type of the communications apparatus can have a directional vector whose direction at the attachment position of the communications apparatus is constant. In contrast, the card type of the communications apparatus has a directional vector whose direction is varied depending on the attachment state (direction or inclination degree, etc in the pocket).
That is, the communications quality may be deteriorated remarkably or the capability may be disabled, depending on the above various states.